Hitherto, a transformer-rectifier device to power an electron-beam device has been a coaxial system comprising an accelerating tube, a sectionalized secondary winding, a sectionalized magnetic circuit, and a primary winding contained within a single metal enclosure. The main magnetic flux indiced by the primary winding partly links the non-magnetic elements of the device and induces in each secondary-winding section an a.c. voltage which is converted to a d.c. voltage by the builtin accelerating tube.
In said transformer-rectifier device, the magnetizing current has a direct component, and the magnetic flux has its path through the nonferromagnetic space of the accelerating tube.
This calls for a power supply of an increased installed capacity and impairs the reliability and service life of the accelerator because the power supply and the electron acceleration section are not isolated from each other under abnormal conditions either physically or electrically.
Another approach has been a high-voltage transformer-rectifier device intended to feed a direct-acting electron accelerator (cf. see USSR Inventor's Certificate No. 500,719, Class H05H5:00, of Oct. 25, 1976, Specialized Design Bureau of the Institute for High Temperatures, USSR Academy of Sciences, Bulletin No. 39, Column 2).
Said device comprises a step-up three-phase transformer with a spatially symmetric magnetic circuit carrying a primary winding and a sectionalized secondary winding.
In said device, rectifier units forming a bridge rectifier are placed parallel to the symmetry axis of the magnetic circuit. One pole of the bridge rectifier is grounded and the other is connected to a potential screen. The neutral point of the high-voltage secondary winding is likewise connected to a potential screen of its own which is insulated from the grounded lower yoke of the magnetic circuit by a support insulator.
The high-voltage terminal of the device is connected to the potential screen of the bridge rectifier pole and is arranged coaxially with the magnetic circuit. An accelerating tube combined with said terminal is installed in the same container as the transformer-rectifier device, filled with sulphur fluoride (SF.sub.6) gas.
In said device, however, the insulation has to withstand unfavourable service conditions due to the off-optimal electric field structure in the effective volume, a high reactance, and a low power factor at an output voltage of several hundred kilovolts.
Thus, the insulation of the device in the direction of its symmetry axis must additionally be designed (like the axial insulation of the secondary winding) to carry the voltage between the secondary-winding neutral and the grounded magnetic circuit, and also twice the full rectified voltage. This impairs the reliability of the high-voltage transformer-rectifier device under likely overvoltages in the system and also under normal service conditions.
In said device, the insulation of the sectionalized phase secondary windings must be designed to withstand the full line voltage because the windings are connected to the rectifier units which are the full arms of the three-phase bridge rectifier. This complicates the radial structure of the electric field in the effective volume of the device. The breakdown of one of the secondary-winding sections constitutes an abnormal condition for the entire device because the magnetic flux is expelled from the spatial magnetic circuit leg common to all the second-ary-winding sections.
Since the insulation between the secondary winding of the step-up transformer and the magnetic circuit is designed to withstand the full voltage, it forms a large leakage channel for the magnetic field, so the reactance and, as a consequence, voltage losses during the commutation intervals of the rectifier units are increased. Practically, the leakage inductance of the transformer is 15% to 20%. This impairs the electrical performance of the device because the external (load) characteristic becomes drooping, and the converter draws a considerable rectifier power due to the increased commutation angle of the rectifier units. Because the high-voltage transformer-rectifier device and the accelerating tube are combined into a single unit and the power supply and the load are not isolated from each other during an abnormal condition, the reliability of the device is impaired and its service life in continuous duty is cut down. The breakdown of, or damage to, any element of the power supply or the accelerating tube calls for dismantling the entire accelerator.